Molding devices are known which use separate transport and locking units. These devices use a relatively low-powered transport unit to move the mold halves into positions near each other and a second high-powered locking unit to provide the locking forces to lock the mold closed. The locking forces are provided by tension couplings attached directly to the mold holders and capable of being moved in the direction of mold travel.
Such locking devices include rigid coupling halves on one mold half which engage hydraulically displaceable coupling halves on the opposing mold half. The two coupling halves engage shortly before the transport device finishes moving the mold halves into a slightly separated position. At this point, the locking device is engaged and activated to transmit the closing and locking forces with an even distribution of the mold closing forces throughout the mold halves.
This type of mold closing and locking device eliminates the deformation forces which would normally act on a machine frame. This allows frameless contruction. Space limitations are overcome to a large extent and distribution of the locking forces on the mold halves is optimized. At the same time, the transport mechanism is simplified and the space inside the machine is optimized.
By mounting the couplings on the mold halves, a closed system of forces is created in the mold halves because the reactions are used as closure and closing forces. The closure forces in the mold halves may be more controlled. This enables the mold halves or fixture plates to be interchangeable. This increases the number of uses for the machine.
In operation, a plastic tube or preform is extruded between the opened mold halves. After the preform has been fully extruded, the halves of the mold are moved toward each other until they are separated by a distance approximately the same as the diameter of the preform. The transport system which moves the mold halves to this position is shut down once the couplings are properly engaged. The hydraulic locking system is then operated to draw the mold halves together and lock them into place. The power of the locking system is great enough to pinch off the preform tube and weld it together at the seams. The coupling members are positioned, depending on the mold in use, to exert uniform action on the halves of the mold. This avoids much of the mold deformation of the Prior Art.
It is seen therefore that the couplings must be designed in such a way to withstand the great locking forces they are subjected to without an overly complex and expensive design.